Apparatus for ammoniation of superphosphate



April 10, 1956 F. T. NIELSSON APPARATUS FOR AMMONIATION OF SUPERPHOSPHATE Filed Nov. 18, 1953 12 IO ll 23 Sum 57. W INVENTOR.

United States Patent APPARATUS FOR Ah/iMONIATION 0F SUPERPHGSPHA'IE Francis T. Nielsson, Shefiield, Ala, assignor to Tennessee Valley Authority, a corporation of the United States Application November 18, 1953, Serial No. 393,024

3 Claims. (Cl. 23-2591) (Granted under Title 35', U. 5. Code (1952), see. 266) The invention herein described may be manufactured and used by or for the Government for governmental purposes without payment to me of any royalty thereon.

This invention relates to apparatus for continuously ammoniating superphosphate.

The treatment of superphosphate with ammonia is practiced widely in the fertilizer industry. Liquid or gaseous anhydrous ammonia, aqua ammonia, or ammoniating solutions containing free ammonia and a solid nitrogen carrier such as ammonium nitrate or urea are employed as ammoniating agents.

The most commonly used type of equipment for ammoniating superphosphate is the rotary batch mixer. A quantity of superphosphate is fed into the mixer, and aqua ammonia or solution is introduced while the mixer is rotated.

A pug-mill type of ammoniator has been developed for continuous operation. The machine consists of a tube having a central shaft on which are mounted blades set at a pitch to move the material forward in a violent state of agitation. Ammoniating solution is sprayed through nozzles set in a recess along the top of the tube.

Among other types of equipment that have been proposed for continuous ammoniation are screw conveyors and ribbon mixers.

Continuous ammoniation of superphosphate in equipment of the type described above can be carried out without undue difficulty when aqua ammonia or an ammoniating solution is used as the source of ammonia. With anhydrous ammonia, however, considerable difiiculty has been encountered. In order to minimize loss of ammonia, it has been the practice to carry out the ammoniation in closed equipment, with gas ofi-takes provided to transfer the evolved water vapor and ammonia to ammonia-recovery facilities. Closed equipment of this type requires sealed inlet and discharge openings and special bearings that are not always efiective and are troublesome from the maintenance standpoint. Moreover, in a closed system the material undergoing ammoniation is always in contact with an atmosphere of water vapor. Condensation of water vapor takes place on the relatively cool superphosphate entering the equipment. The amount of Water condensed is sufficient, usually, to turn the superphosphate to a thick, pasty mass which soon clogs the equipment. Conversion of a part of the P205 to a form unavailable to plants also occurs during ammoniation.

It is an object of this invention to provide apparatus condensation of water vapor takes place and the product is obtained in coarse granular form.

Still another object is to provide an apparatus requiring no inlet or discharge sealing means.

Other objects and advantages of the invention will be come apparent as this disclosure proceeds.

I have found that these objects may be attained in a device of the class described, which comprises in combination an inclined rotary cylindrical drum; two retaining rings singly disposed at the ends of the drum; an ammoniadistributing member having a length almost equal to that of the drum between retaining rings disposed within the drum near an inner wall and substantially parallel to the axis thereof and about 20 to 40 from a vertical diameter in the direction of rotation of the drum; and means for passing a current of air through said drum.

In the accompanying drawing, Figure l is a vertical view depicting components of one preferred device embodying principles of my invention; Figure 2 is a vertical sectional view of the rotary drum ammoniator taken along the longitudinal axis thereof; Figure 3 is a sectional view taken on line 3-3 of Figure l; and Figure 4 is a sectional view taken on line L-4 of Figure 2.

Referring to Figure l, the numeral 10 designates a rotary drum having open ends and fitted with tires 11 and spur gear 12. Drum 10 is mounted on trunnions 13 and driven through gear 14 by a motor (not shown) Numeral 15 designates a feed chute which is adapted to convey super-v phosphate from feeder-conveyor 16 to the interior of drum 10. Ammonia-containing fluid from a source not shown is fed to manifold 17 mounted Within drum 11) via control valve 18 and flexible conduit 19.

Water for cooling purposes is introduced via valved line 20. The portion of line 20 within the drum is perforated so as to direct a spray of water onto the material in the drum. A means for passing a current of air through the drum is provided and is illustrated as hood 21, duct 23, and fan 24. Any other means for passing air over the surface of the bed may be substituted for the means illustrated if desired, for example, jets of compressed air directed into the drum to induce such flow, a blowertype fan disposed to force air across the bed by slight positive pressure; a suction pump operated by flow of waste water, or steam ejectors may be substituted for suction fan 24, or any other arrangement desired. The type of equipment for passing air through the drum is immaterial to the present invention; it is merely necessary that some means for doing so be provided.

Hood 21 is disposed about the lower end of the drum 10. The lower portion of hood 21 is adapted to conduct ammoniated superphosphate discharged from the drum 10 to product conveyor 22. Duct 23 at the upper end of hood 21 communicates with fan 24 and stack 25. Fan 24 induces a flow of air through drum 10 and discharges this air, laden with moisture and any fumes evolved in drum 10, to the atmosphere.

Figure 2, a longitudinal, cross-sectional view of drum 10, shows retaining rings 26 and 27 disposed at the feed and discharge ends, respectively, of the drum to main tain a bed of material of substantial depth therein. Ammonia distributing member 29 is disposed near the lower inner wall of drum 10 well beneath the surface of the bed of material at a location from 20 to 40 from a vertical diameter in the direction of rotation of the drum and parallel to its axis.

"Manifold 17 is disposed along the axis of drum 10. Communicating with manifold 17 are supply tubes 28 which in turncommunicate with slotted distribution member 29. 4

In Figure 3 the dotted line 30 designates the level of the bed of material within drum 10. Arrows show the flow of material within the bed of material. It is to be m mber 29, comprising a'length'of piprhaving closed ends. 'Supp1ytubes'28 communicate Withthis pipe near the ends thereof. 'Holes 31iare drilledat intervals' through thewall of" the pipe. "The size -of these holes is graduated, Withrthe smallest holes at the ends of the'pipeandthe largest holes at thevcenter. Opposed plates '32 are secured to the pipe so that the assembly presents -minimum-rer sistanc'e to theflow of material pastthedistributor and V to' fqrm a'constrictedrslot 3'3that extends'thelength of the-distributor. The-ends ,ofthe distributor-are closed.

"The combination of'the graduated=size holes and the constricted slot gives ajflow of ammoniating-fiuid-from the distributorthat increasesuniiormly'fronr a minimum atzthe ends of the ldlStl'lblltOl" to :amaximumat the center.

In operation, superphosphate is 'fed at a constant rate by feeder-conveyor '16 into chute and into drum "'10.

A bed of superphosphate having a depthequal to about d one-fourth to two-fifths of the diameter of the drum :is maintained within the drum by retaining ring 27-at 'the discharge end ot-the'drum. Material-iskept-fromspilling out of the feed end ofthe .drum by retaining ring26.

' Rotation ofthe drum causes the bedto'assum'e the configuration indicated by numeral in Figure 3. The steepness of the inclination ofthe bed depends, of'course, upon the speed of rotation. Preferablyflhe speed of rotation is such that the inclination is between 30 and 45" 'tothe horizontal. 'Undersuchconditions there is arelatively thick layer of material moving upward at a speed slightly less than'the peripheral speed ofthe drumtand a relativelythinlayer of material at the surface of the bed moving downwardly at a substantially greaterspee'd. This action causes a thorough mixing of-themater'ial in the drum and causes each particle of superphosphate-toibe exposed to ammonia a number of times-as it'progresses from-the inlet-to the outlet of the drum.

iimmoniating fluid fed into manifold 17 at a constant rate passes through supplytubes 28 into the slotted distribution member 29. The rate of introduction of ammoniating fluidis regulated according to therate of introduction of superphosphate and the amount 'of nitrogen desired inthe product. The fluid-leaves theslotted mem her in a broad, rihbonlike stream-parallel countercurrentyto the movement of materialin the *bed. The rate at which the fluid is introducedinto thebedisgreatest at the center of the member and diminishesgraduallyto a minimum at either end of the'member. j

"The reactions that take place during ammoniationof the superphosphate are exothermic, and theheat'liberated causes vaporization of some of the water present. A how of air through the drum,'induced-=by fan'2'4, carries'oii this water vapor. Were this water vapor not removed, condensation would take place on the incoming superphosphate, turning -it to a thick, pasty-mass.

"At times, particularly when anhydrous'ammoniaisbeing used, it is necessary to spray asmall amount ofwateronto thebed to cool the-material. Overheating :o'fthe materialv causes excessive reversion of available PzQs toannnavailable form. It'isnQtnecessaryto spray'water'when aqua ammonia or ammoniating solutionis-used.

' proximating -a flattened helix. -Ammonia is introduced beneath the surface of the bed at a multiplicity of points in the path of each particle. This results in a slow and continuing absorption of ammonia. It is to this slow and continuing absorption of ammonia that I attribute the low losses of ammonia and the low reversion of P205 to unavailable form that characterize results "obtainable in my apparatus.

Studieshave shown that by.mynovehmocessand-ap: paratus either anhydrous ammonia, aqua :ammonia, -'or ammoniating solution can be employed without significant loss of arnnronia. Thave also foundthatbymy-process and apparatus it is possible" to fix;substantially greater proportions of free ammonia than are fixed by prior processes and apparatus and that reversion-of available P205 to unavailable form is less in my process than in prior processes. A further advantage of .myinvention is that a large proportion or the superphosphate treated is converted to a desirable granularfform.

Tests oif my invention were carried outinan experimental ammoniator '3 feet'in diameter'by '3ffeet long, .constructed according to the attached drawings. 'The .drum hadQ-inch retaining rings at either end, leaving circular openings '18 inches in diameter. 'The drum wasinclined downwardly from feed end todischarge end'atan angle 053* to the horizontal. The-drum was rotated at afspeed of 10 revolutions per minute.

A slotted ammonia-distribution member, constructed shown in .Figure 4, waszpositione'd within the 'drum as described.

Example I Tests of.my invention were carried out .on the treatment of concentrated superphosphate with gaseous anhydrous ammonia. "The .feed .s'uperphosphate was made from P205 and 146.5 per .cent available P205. The superp'hos- 'Ammtmiated superphosphatedisc'harged'from'rlrum10 is conveyed to storage or cooling facilitiesby conveyor 22.

A significant diiference between the operation ofmy apparatus and prior processes lies, in the fact that-each particle "of superphosphate comes "-in "contact with 1ammoniating fluid many times during its passage throughthe ammoniating zone. Although the particles introduced form a bed, the individual particles are passedithrou'g'hphate was fed .to .the experimental ammoniatorat arate of 100.0 poundsper .hour. 4

' In order to obtain a comparison between the efiectiveness of the, experimental ammoniator and conventional equipment, tests were also carried out in a'batchmixerof the type used commercially ffor .ammoniating superphosphate. The batch mixer was 5 'feet .in .diameter.and '5 feet'long. The'batch mixer was loaded with v10010 pounds of concentrated supexphosp'hate, and anhydrousammonia was introduced beneath the bed .of materialimthe mixer. Ammonia was introduced over a period of 2 minutes to attain 4 m cent 'N in product and 91) minutes .to attain N=contents higher. than 4 per cent in product. Thematerial was allowed to remain in the drum for minutes.

.Iheffdllowing table gives the results of these .tests.

' 'Inltestsin whlohmore than 7-percent nitrogen was introduced intozthe product, water :wassprayedbntzo thematerial :iu thetammoniator.

.These .tests demonstrated that I with the -.experimental ammoniator it was possible to .ammoniate snperphosphate toa higher degree than was possible with theconventional batch ammoniator. At the same time, reversion of P205 to unavailable form and loss of nitrogen were lower with the experimental ammoniator at comparable degrees of ammoniation.

Other types of ammoniating equipment were tried, including a closed ribbon mixer, but in all cases loss of available P205 and loss of nitrogen were higher than with the experimental ammoniator.

Example II Comparative tests were also made on the preparation of a high-analysis mixed fertilizer using ammoniating solution, ammonium sulfate, ordinary superphosphate, and potassium chloride. These ingredients were fed to the experimental ammoniator and to the batch mixer in proportions to give a product having a ratio of NzPzOstKzO of approximately 1:1:1.

The superphosphate in the mixture fed to the experimental ammoniator contained 20.5 per cent total P205 and 19.6 per cent available P205. The supeiphosphate in the mixture fed to the batch mixer contained 19.3 per cent total P205 and 18.1 per cent available P205. The ammoniating solution used in both tests contained 55.5 per cent NHrNOs, 26 per cent free NHs, and 18.5 per cent H20. The feed rate of solid materials to the experimental ammoniator was 1000 pounds per hour. Batches of 1000 pounds of solid materials were loaded into the batch mixer. The results of these tests are given in the The results of these tests showed that although the batch m'mer was more efhcient when operated with ammoniating solution than with anhydrous ammonia, losses of free ammonia and available P205 were still much higher with the batch mixer than with the continuous experimental ammoniator.

Example 111 Tests also demonstrated that by my process and apparatus the ammoniated product was obtained in granular form. The following results were obtained in a series of tests in which concentrated superphosphate was treated with anhydrous ammonia and in which water was sprayed onto the material within the drum at a rate of 5 to 6 pounds of water per 100 pounds of superphosphate.

Screen analysis, U, s, Nitrogen standatd, percent Material content,

Percent 50 +4 mesh mesh mesh Tests were also carried out in which concentrated superphosphate was treated with ammoniating solution containing 26 per cent NHa, 55.5 per cent NHQNOS, and 18.5 per cent H20. The following results were obtained.

In all these tests the product was in the form of hard, well-rounded granules.

Example IV The equipment was operated continuously in a run of 20 hours duration at a rate of 1800 pounds of ammoniated product per hour. Ordinary superphosphate and potassium chloride were added to the ammoniator at rates of 1000 pounds per hour and 550 pounds per hour, respectively. Ammoniating solution (55.5% NHtNOs, 26.0% neutralizing ammonia, 18.5% H20) was added at a rate of 23r pounds per hour to yield a product containing 6.8 per cent N, 11.6 per cent available P205, and 12.6 per cent K20. Loss of P205 availability was 0.9 per cent and loss of neutralizing ammonia was 3.4 per cent. The degree of ammoniation (6.7 lbs. neutralizing NI-Ia per unit available P205 in the feed) was considerably higher than the ratio recommended by suppliers of ammoniating solution (2.5-3.5 lbs. neutralizing NHs per unit available P205 in the feed). No cleaning of the ammoniator was required during this operating period.

Various modifications of the ammonia-distributing member may be substituted for that shown and described, if desired. For instance, plates 32 might be omitted a1- though they are well worth their cost, both in securing even distribution of ammonia and in preventing clogging of holes 31; or the member might be made without a wall between the interior of the tube shown in Figure 4 and the space limited by plates 32, provided that slot 33 is constructed with sufiicient accuracy.

It also has been found technically feasible to spray sulfuric or phosphoric acid (but not nitric) on the superphosphate bed during ammoniation to obtain greater degrees of ammoniation through neutralization of the acid and, because the water vapors evolved have been carried away, a dried product results in which ammonium phosphate or ammonium sulfate had been formed in situ. When acid is introduced, best results have been obtained when an acid distributor is located just below the surface of the material in the bed. If much water be introduced, as when the acid is in dilute solution, it may be necessary to pass additional air through the ammoniator to carry off excess water vapor.

Other modifications may be made without departing from the spirit of the invention, which is limited only by the subtended claims.

This application is a continuation-in-partof my copending application Serial No. 328,156, filed December 26, 1952, and the apparatus claimed herein is particularly adapted to use in carrying out the process of that application.

I claim as my invention:

1. A device of the class described which comprises in combination a rotary cylindrical drum having open ends and length substantially equal to its diameter disposed with its axis inclined from the horizontal about 3 degrees; two retaining rings singly disposed at the ends of the drum;,a stationary manifold disposed within the drum and along the axis thereof; a valved conduit communicating with the interior of the manifold, adapted to introduce ammoniating fluid into the manifold at controlled rate; a distributing member comprising a pipe of length substantially equal to the length of the drum between retaining rings disposed within the drum substantially parallel to the axis thereof, .near vtheinner surface of the .drum' about 20 degrees to 40 degrees from the intersection of l a vertical fdiameter with the bottom of the drum in the direction ofrotation the pipe having closedends and a of the pipe attached to the pipe -on-either side of the series of openings at converging angles to'form'anarrow slotalong the side of the distributing" member oppos'ite'to V the direction of rotation ofthe "drum," and supply tubes disposed to communicate with saidmanifold 'and'sai'd pipe; and means, comprising afan, for passing a current of air through said drum. g

/ 2. A device of 'thefclasfdescribed tvhich'comprises-in combination "an inclined rotary -cylindrical drum having open ends and lengthsubs't'aritially equal to itsidiameter; two retaining rings s'ingly' disposed at the ends of 'the drum; a stationary manifold disposed Within the drum and along the axis thereofyavalved conduit communicating with the interior of the manifold, adapted'to introduce ammoniating fluidinto the manifold at controlled rate; a distributing member comprising a ,pipe of length substantially equal to the length of the drum between Vreraining rings disposed within the drum 'substantiallyparalle'lto the' axis thereof, near the inner surfaceof the drum about 20 degrees to 40 degrees fromfthe intersection of a vertical diameter with"'thebottom of the drum in the direction of rotation, thep'ipe having closed ends and a series of openings alongits' side opposite to' the direction ofrotation of the drumgtheser'ies of openings increasing in area from the ends of the ;pipe'-to the center thereof, two opposed plates of leng'th substantially-equal to that of-thepipe attached to'theipipe on either side of theseries of-openingsat converging angles to form a --narrow slot along the side of the distributing member opposite to the direction of rotation of the drum, and =supply-tubes dis? posed to communicate with said manifold'andsaid'pipe; I

and means for passing a current of air through said drum.

3. Adeviceof the class described which' comprisesin combination-an inclined rotary cylindrical 'drum having open ends; two retaining rings singly disposed-at the ends of the drum; a stationary manifold disposed Within the drum and along the axis'thereof; a valved conduit communicating with the interior of the manifold, adapted to introduce ammoniati'ng fluid into the manifold at 'contr'olledtate; a distributin g me'mber comprising a'p'ipe of length-substantially equal to the length 'of the 'driim between retaining rings disposedwithin the drum s'ubstan tially 'parallel to the axis'thereof, near the innersur face of thedrum about 20 degrees to 40 degrees from "the intersection of a vertical diameterwith the bottom "of the rlrum-inthe-dir e'ction of rotation, the pipe having closed ends anda series of openings along its side opposite to the-direction of rotation of'the drum,-the series of openin'g's increasing in area from the ends-of thepipe to the 3 center thereof, and supply tubes disposed to communicate with said manifold and said pipe; and means for passing a current of air through said drum.

References Cited in the file of this patent V UNITED STATES PATENTS 481K506 

1. A DEVICE OF THE CLASS DESCRIBED WHICH COMPRISES IN COMBINATION A ROTARY CYLINDRICAL DRUM HAVING OPEN ENDS AND LENGTH SUBSTANTIALLY EQUAL TO ITS DIAMETER DISPOSED WITH ITS AXIS INCLINED FROM THE HORIZONTAL ABOUT 3 DEGREES; TWO RETAINING RINGS SINGLY DISPOSED AT THE ENDS OF THE DRUM; A STATIONARY MANIFOLD DISPOSED WITHIN THE DRUM AND ALONG THE AXIS THEREOF; A VALVED CONDUIT COMMUNICATING WITH THE INTERIOR OF THE MANIFOLD, ADAPTED TO INTRODUCE AMMONIATING FLUID INTO THE MANIFOLD AT CONTROLLED RATE; A DISTRIBUTING MEMBER COMPRISING A PIPE OF LENGTH SUBSTANTIALLY EQUAL TO THE LENGTH OF THE DRUM BETWEEN RETAINING RINGS DISPOSED WITHIN THE DRUM SUBSTANTIALLY PARALLEL TO THE AXIS THEREOF, NEAR THE INNER SURFACE OF THE DRUM ABOUT 20 DEGREES TO 40 DEGREES FROM THE INTERSECTION OF A VERTICAL DIAMETER WITH THE BOTTOM OF THE DRUM IN THE DIRECTION OF ROTATION, THE PIPE HAVING CLOSED ENDS AND A SERIES OF OPENINGS ALONG ITS SIDE OPPOSITE TO THE DIRECTION OF ROTATION OF THE DRUM, THE SERIES OF OPENINGS INCREASING IN AREA FROM THE ENDS OF THE PIPE TO THE CENTER THEREOF, TWO OPPOSED PLATES OF LENGTH SUBSTANTIALLY EQUAL TO THAT OF THE PIPE ATTACHED TO THE PIPE ON EITHER SIDE OF THE SERIES OF OPENINGS AT CONVERGING ANGLES TO FORM A NARROW SLOT ALONG THE SIDE OF THE DISTRIBUTING MEMBER OPPOSITE TO THE DIRECTION OF ROTATION OF THE DRUM, AND SUPPLY TUBES DISPOSED TO COMMUNICATE WITH SAID MANIFOLD AND SAID PIPE; AND MEANS, COMPRISING A FAN, FOR PASSING A CURRENT OF AIR THROUGH SAID DRUM. 